Abstract: The prefabricated steel structure is highly efficient in construction because of its industrial production and modular installation． The structure is different from the traditional steel frame and its dynamic behavior under earthquake needs． The elasto-plastic dynamic time history analysis was conducted for the prefabricated steel frame structure with and without inclined support joints under 7 degree earthquake． The results showed that the overall stiffness of structure increased greatly because of the inclined support joints and the deformation was reduced obviously under the 7 degree earthquake and the top maximum displacement of the structure was reduced by 56. 6% while the maximum interlayer displacement angle was reduced by 61. 3% under artificial waves，most of the plastic hinge appeared in the webs of the truss girder and the columns were in elastic stage．